Aleph 5 bias

[billy]

Hello, i have some questions of R19 , i know that if i reduce the value of R19 then the bias will down, but how about the bias if i jumper the R19? can i do that ?

Thanks!!

 

[Mark A. Gulbrandsen]

I don't quite understand why you want to do that. I doubt the amp would work at all with it shorted out. Raising the resistance of R-19 increases the bias, and the current through the devices. Lowering the bias does exactly the opposite and the result would be poor linearity of the amplifier.
Mark

 

[Leeuwarden]

I don't quite understand why you want to do that. I doubt the amp would work at all with it shorted out. Raising the resistance of R-19 increases the bias, and the current through the devices. Lowering the bias does exactly the opposite and the result would be poor linearity of the amplifier.
Mark

Mark,

Doesn't Billy mean: leaving R19 out instead of using a jumper?

Greetings

Jan

 

[Mark A. Gulbrandsen]

I hope thats what he means....I don't know what would happen if R-19 was jumpered....would it not operate, or would it suffer catastrophic failure???
Mark

 

[dantwomey]

I'm building an Aleph 5 with double the heaksinks that are required. How high do you think I could raise R19?

Regards,
Dan

 

[Mark A. Gulbrandsen]

I'd say put in a pot of 200K to adjust it up and keep checking the device temp to be sure its within limits. In my case I just left R-19 out completely, but not until I listened to them at various bias levels. Things really get cook'n at the higher bias amounts!
Mark

 

[roddyama]

The rule of thumb has been that each output device should disipate a maximum of about 30W. Nelson Pass warns that above this, the failure rate will go up quickly.

Rodd Yamashita

 

[Lucas_G]

Hi Biased Guys,

I pu up a question regarding the use of R19 in this thread:

http://www.diyaudio.com/forums/showthread.php?postid=159195#post159195

Hopefully it will shed some light on this....

Lucas

 

[wuffwaff]

Dan,

over a certain value R19 won´t be doing anything (same as leaving it out). This will give you between 2.2 and 3 A depending on used fets.

If you want more you´ll have to use source resistors that are lower in value (0,68R or 0,47R), put in R19 again and fine tune with this.

I think it´s no problem to go over 30watts per device as long as your heatsinktemperature is low enough and the fets are still in the safe operating area. I would stay below 100°C but they are specified for 150°. I think Nelson said something like "using them at 50watts on a 70° heatsink will see some failures"

For an Aleph 5 with 6 fets this means you can easily dissipate 180-240 watts per channel (bias is then watts/powersupplyvoltage).

william